1, food colorants: food coloring for the primary purpose of food additive called stain, also known as pigment. 2, according to sources: including synthetic food colorants and two types of natural food coloring agent. 3, in terms of structure: synthetic food colorants can be classified as azo-colorants and non-azo colorants; 4, natural food colorants can be divided into pyrrole, multiple classes, one class, Quinones, and polyphenols. 5, according to the solubility of stains: can be classified into fat-soluble and water-soluble.